Constrained layer damping vs mass loading in speaker cabinets.

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Hobbsmeerkat

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I've seen videos talking about Constrained Layer Damping (CLD) for use in speakers to help reduce cabinet resonance, often using a rubber/tar-like adhesive between two layers of plywood/MDF, etc. For example, using Sorbothane or Decidamp between the layers to absorb the motion instead of transfer it.

How does that differ from situations like Mass-loading with products like Norez, Lizard Skin, and Dynamat, which also absord vibrations, but without a second rigid body on the opposite side.
What about a cabinet that's walls are filled with sand/kitty litter?

Are they fairly comparable, or are there situations when one or the other are preferable? Or is it more a choice among the compromises you're willing to make?

Martyn

Damping treatment typically consists of a material that's applied to the surface of a vibrating object in order to increase its ability to dissipate energy. Damping is most effective at and around the resonant frequency of the object. If you read the academic and industrial white papers on this subject, the typical applications are for the damping of thin material such as car body panels or the enclosures of mechanical equipment. Sticking a piece of Dynamat on the inner surface of your car's door skin will work wonders (unless the manufacturer has already done that).

Constrained layer damping is typically applied to structures that are already relatively stiff, such as a well-designed speaker cabinet. The key here is that the energy-absorbing material sandwiched in the middle of the surrounding plies of a panel must be attached to the panel skins with high shear strength. This means that filling the sandwich with some low durometer elastic material isn't going to work as constrained damping. The stuff provides little shear resistance and thus doesn't absorb much energy.

I once built a pair of 3-way speakers with hollow panels which I filled with play sand. It's extremely labour-intensive and needs careful structural design. Nonetheless, it worked very well and produced an extremely "dead" cabinet. I'm tempted to try it again from time to time, but only until I remember how much work was entailed.

A simpler approach by far is just to brace the living daylights out of your boxes. Use lots of horizontal braces together with longitudinal shelf braces 2" wide by 3/4" thick. To some extent, your drivers and ports will dictate how close together your braces can be, but try to keep your panel spaces between bracing in the 4" to 6" range. Make sure you allow for the volume of your braces when you calculate the size of your box.

WGH

"The Audibility Of Cabinet Panel Resonances and Pat. Pend. Method Of Reduction Of Audible Coloration" by Albert Von Schweikert, Chief Design Engineer, VSA Corp.

This paper seeks to inform the reader of a new Pat. Pend. design now utilized on all Von Schweikert Audio speaker systems, using a triple layer of constrained damping materials with opposing Q factors.

https://www.audiocircle.com/index.php?topic=70291.0


Martyn

That's an interesting paper. In essence, VS uses well-established materials in a "special" combination in order to apply for patent protection.

Manufacturers all face the same couple of problems. First, they are all putting drivers into a box, so how do they differentiate themselves from all the others? Second, having differentiated themselves, how do they prevent others from copying them and thus destroying their differentiation? Well, they can prevent commercial operations from copying them (up to a point) by getting patent protection, and they can prevent the DIY crowd from copying them in their garages by introducing manufacturing methods or materials that are hard for the DIY guys to replicate. I don't have the time to dissect the VS paper in detail here, but suffice to say that I suggest that this is all that's going on here.

From a materials perspective, we're all familiar with MDF, which VS uses as the outer skin. "Synthetic stone" has been around for a long time and is used at a very high level of refinement by Studer for machine tool bases and for the bases of co-ordinate measuring machines - it is dense, stable, and has good inherent damping. In the world of noise control, high "surface mass" is the key to high transmission-loss through a material; synthetic granite is pretty good at this, although not as good as lead. VS sticks the stone to the MDF with a thick layer of rubbery material, so he's mass-loading it (it's not constrained layer). On the inside he uses what appears to be a layer of bitumen-impregnated felt; this is a material that was used inside British speaker boxes in the 1960s. Finally there's the "Gradient Density Damping" - an impressive trade-marked term for Dacron that's packed tighter against the wall and looser on the inside.

None of this is to say that this "pat pending" construction isn't effective - just that it's not necessary in my opinion. If you want to build an effective cabinet that you don't need a forklift truck to move around, try to drive those panel resonances into the high frequency range where they can be damped easily - so lots of bracing to create small, stiff panels. Avoid parallel walls as much as you can, especially for the mid-range enclosure. Find some of that 2" thick yellow rigid fibreglass that the construction industry uses (not the fluffy insulation for wall cavities) and stick a slab of it to the back wall behind the mid-range and woofer, and to the bottom of the box to help with that annoying standing wave.

I built my most recent speakers with a pentagonal cross-section and a pyramid-shaped mid-range enclosure (complicated woodwork, not for the beginner). The pentagonal shape eliminates parallel walls and also makes them a bit narrower than with four walls. A vertical brace down each one stiffened them further. I used lots of horizontal braces, each with a different pattern of routed cut-outs. The top and bottom panels are double thickness. Each cabinet came in at 55 lb bare (in Baltic Birch) and 71 lb in total, so very manageable. A couple of weeks ago, I listened to a pair of Sonus Faber floor-standers fed from a Sim Moon streamer via a McIntosh amp - I think my speakers fed from a Squeezebox through a miniDSP and an old Arcam AVR sounded better.

Sorry if this rambled a bit, but I've learned over the years that good box design beats technical wizardry.

JLM

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Have been a transmission line (TL) fan for 40+ years, thanks to Irving (Bud) Fried (built 6 cubic foot TL bass Fried cabinet kits long ago) and 16 years ago commissioned TL speakers that i still use and enjoy.  Fried built very musical speakers and his TL designs were very powerful.  TL address cabinet stiffness and non-parallel panels by their inherent design.  My speakers also slant the panel directly behind the driver that directs the back wave away from bouncing back out through the driver (a major flaw of most speaker designs IMO).  If you think about it, the driver cone is by far the weakest link in the cabinet enclosure. 

Martyn, agree with much of what you've stated, but will save my verbiage for another time.   :thumb:

Martyn

If you think about it, the driver cone is by far the weakest link in the cabinet enclosure. 


I agree. Getting a few more reflections of that back wave before it hits the cone again will absorb a lot more of the energy. Any cross-sectional shape with an odd number of side will help with this, but a quadrilateral with a sloping back might be easier to build! Before committing to a complex design, I built a rectangular test box. Here's the mid-range enclosure:





The nice thing about this is that Sketchup makes it relatively easy to make, because you can print a dimensioned drawing of each part. It still needs careful woodwork, but it's a lot easier than having to figure out the trigonometry long-hand. This is within the scope of most hobby woodworkers, but is too labour-intensive for commercial manufacturers to be bothered with. In other words, it's an area where the DIY guys can enjoy an advantage. Perhaps this will inspire a few DIY builders...

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BobM

three words "Black Hole Five"

bardamu

Hello,
Just my two cents.
 The French( who brought us Hiraga and Verdier turntable, actually this group of people!) have published a magazine ( L''Audiophile) for a few decades.
Once they published the design of a big bookshelf 2 way speaker with most panels consisting of two panels with different thickness less than half inch with dry sand in between. The sand have more value than the wood.
Their philosophy ( with them it was never just another idea):
In order to make the sand '' work '' one shouldnt use wood with normal thickness ( one inch or so)  You want the panels to have some vibrations to start with and THEN make the sand take care of the vibrations.
Of course this is limited by the seize of the loudspeaker cabinet. They also made the famous Onken with two 15 inch speakers. There also sand inside but thicker panels ( 1inch or so) but that is necessary with this seize of speaker.
They also wrote about '' coupling '' the magnet of the loudspeaker to item that have great mass ( they tested diiferent shapes and materials)
Greetings, Eduard

JLM

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I've seen videos talking about Constrained Layer Damping (CLD) for use in speakers to help reduce cabinet resonance, often using a rubber/tar-like adhesive between two layers of plywood/MDF, etc. For example, using Sorbothane or Decidamp between the layers to absorb the motion instead of transfer it.

How does that differ from situations like Mass-loading with products like Norez, Lizard Skin, and Dynamat, which also absord vibrations, but without a second rigid body on the opposite side.
What about a cabinet that's walls are filled with sand/kitty litter?

Are they fairly comparable, or are there situations when one or the other are preferable? Or is it more a choice among the compromises you're willing to make?

CLD and use of absorbent linings is two different matters and shouldn't be confused.  Design of CLD can be done, but far more complex than any cabinet maker would be expected to take on.  So the best you could do is trial and error, mock up a variety of identical internal configured cabinets with different materials/designs and compare/measure.  Most designers would vote for the deadest possible cabinet (at the frequencies involved).  Consider the bonding strength (shearing resistance) between layers, in which case something like wood/drywall with construction adhesive comes to mind.  Another idea is the careful use of expanding rigid foam. 

Most absorbent speaker cabinet linings are only effective at higher frequencies.  If you look into room treatment absorption you'll find few effective materials and most that are effective are considered too thick for use in speaker cabinets.  That brings us back to controlling back waves via the cabinet shape like transmission lines, rear loaded horns, or quarter wave tuned pipes which typically will also affect the performance of the speaker while redirecting the back wave away from the driver. 

gab

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charmerci

Re: Constrained layer damping vs mass loading in speaker cabinets.
« Reply #10 on: 13 Jul 2020, 07:40 pm »
I remember decades ago that some speaker company was making loudspeaker enclosures out of concrete. A quick look shows that there are a few companies doing that now!

FullRangeMan

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Re: Constrained layer damping vs mass loading in speaker cabinets.
« Reply #11 on: 13 Jul 2020, 08:33 pm »
Years ago I made a HDF pro-audio tall sealed speaker around 150kg. All this mass resulted in no cabinet resonance and a solid soundstage, but this mass no increased the bass by it self, I had to test various materials as stuffing.

rajacat

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Re: Constrained layer damping vs mass loading in speaker cabinets.
« Reply #12 on: 13 Jul 2020, 10:00 pm »
I built my 85 lb. speakers using CL and 1"+ walls. It was a lot of work. In hindsight I'd forgo the CL and use more internal bracing instead.



ginetto61

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Re: Constrained layer damping vs mass loading in speaker cabinets.
« Reply #13 on: 14 Jul 2020, 08:48 am »
I built my 85 lb. speakers using CL and 1"+ walls. It was a lot of work. In hindsight I'd forgo the CL and use more internal bracing instead.

Hi !  this is very nice indeed.  When i will have more time i would like to build something similar ... it must sound phenomenal.
However i would try to decoupled mechanically in some way that i do not know the horn from the bass cabinet.  The woofers especially the powerful ones are beasts ... and beasts need to be put in a cage alone.  The woofer always transmits some kind of vibes to the other more delicate drivers.
I would have no problem to have the horn driver completely exposed and put out of the box ... i usually listen in the dark

Speaking of cabinet damping nothing beats lead ... i know ... it is very toxic to work with  But some years ago me and a friend glued and stapled some lead sheets    
to the internal sides of two Dynaudio msp 110 speakers i still have here (i should replace the woofers with other ones better but i am scared by the lead inside  :?)

They got very heavy indeed.  Very. 
The effect on the sound was terrific ... the instruments with a lot of bass content sounded completely out of the box and extremely clear
Like all the rest of the instruments by the way
At a point the sound was so out of the cabinets that i thought like the speakers were disconnected   :o
I take off the cables and of course the sound disappeared.
What i mean is that since then i am very convinced that mechanically dead speakers sound much better.  Another thing ... clearly front panels are the very critical sides.  Some kind of bolts blocking the front and the rear panel can help a lot in keeping the front baffle still also during loud passages with high low Hz content (i.e. like when listening a Toccata e Fuga played on a big pipe organ). 
The side panels are very much less critical.  The sound coming from a side panel for its vibration is very low in level especially when reaches the listener after some wall reflections.  But vibrations on the front panel can mess up the sound.   

rajacat

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Re: Constrained layer damping vs mass loading in speaker cabinets.
« Reply #14 on: 14 Jul 2020, 03:00 pm »
@ginetto61
Actually the the waveguide/tweeter is in a totally separate cabinet sitting on Herbie's thin Fat Dots. I can adjust the tweeter to match the phase of the woofer. Also I can change out the waveguide for another WG or horn if desired.
      Briefly I toyed with the idea of using lead tape as the constrained layer damping. However, lead lacks the ability to move unlike other CL materials therefore isn't the best for CL. I used Sikaflex for the CL layer after reading about another builder that did some tests of various materials. It's incredibly strong but still can move enough to dissipate vibrations.
It was very tedious gluing the panels together and added a lot of time to the build. I still might use lead tape to further dampen the waveguide.

JLM

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Re: Constrained layer damping vs mass loading in speaker cabinets.
« Reply #15 on: 15 Jul 2020, 11:24 am »
Finally occurred to me that I use CLD everyday:  the ceiling/roof of the center section of our house is made up of SIP's (Structural Insulating Panels).  The SIP's are simply styrofoam glued between two sheets of OSB (or could be plywood, even foundation grade plywood).  Provides great strength, as a structural engineer had to prove it to myself, (our's span 16 feet across the roof) and superior insulation (no gaps due to studs).  A whole house could be built of it in which case the house would thermally perform like a plywood refrigerator (super insulated).  The styrofoam can be up to whatever thickness is available (12 inches last I knew) and the sheets are available up to 8 feet x 24 feet. 

Often SIP's are used in conjunction with post and beam framing.  The concept was developed in the 30's by the forest service to conserve lumber (since the plywood/OSB is made up of left over/lower quality wood chips).  Houses made of SIP's can be erected quickly.  Cost is comparable with other methods of well insulated homes.  The biggest challenge is careful preplanning and commitment of window/door openings.  Another obstacle is running wiring, although "conduits" are cut/melted into the styrofoam at regular intervals but residential electricians unlike snaking wire through them.  Several proprietary methods are used for joining the panels together. 

Peter J

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Re: Constrained layer damping vs mass loading in speaker cabinets.
« Reply #16 on: 15 Jul 2020, 03:16 pm »
Finally occurred to me that I use CLD everyday:  the ceiling/roof of the center section of our house is made up of SIP's (Structural Insulating Panels).  The SIP's are simply styrofoam glued between two sheets of OSB (or could be plywood, even foundation grade plywood).  Provides great strength, as a structural engineer had to prove it to myself, (our's span 16 feet across the roof) and superior insulation (no gaps due to studs).  A whole house could be built of it in which case the house would thermally perform like a plywood refrigerator (super insulated).  The styrofoam can be up to whatever thickness is available (12 inches last I knew) and the sheets are available up to 8 feet x 24 feet. 

Often SIP's are used in conjunction with post and beam framing.  The concept was developed in the 30's by the forest service to conserve lumber (since the plywood/OSB is made up of left over/lower quality wood chips).  Houses made of SIP's can be erected quickly.  Cost is comparable with other methods of well insulated homes.  The biggest challenge is careful preplanning and commitment of window/door openings.  Another obstacle is running wiring, although "conduits" are cut/melted into the styrofoam at regular intervals but residential electricians unlike snaking wire through them.  Several proprietary methods are used for joining the panels together.

I don't know that SIPs would be considered CLD. My rudimentary knowledge of CLD is that the constrained layer would be viscoelastic in nature. I question whether expanded polystyrene exhibits these properties.

The whole concept is interesting to me. Enough so that if someone were willing to do the measurements of samples and draw conclusions, I'd be willing to make test samples. With stuff I have on hand I could make vacuum bagged SIPs-like panels from EPS and XPS foam, as well as 8# density two component poly foam constrained by fixed skins.

Any scientific types willing to jump in with me? I don't have the technical knowledge or apparatus for that portion.

Speedskater

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Re: Constrained layer damping vs mass loading in speaker cabinets.
« Reply #17 on: 15 Jul 2020, 05:09 pm »
I don't know that SIPs would be considered CLD. My rudimentary knowledge of CLD is that the constrained layer would be viscoelastic in nature. I question whether expanded polystyrene exhibits these properties.

The whole concept is interesting to me. Enough so that if someone were willing to do the measurements of samples and draw conclusions, I'd be willing to make test samples................................ ..............................
Any scientific types willing to jump in with me? I don't have the technical knowledge or apparatus for that portion.
No, it would be just the opposite. It's an extremely stiff lightweight construction.

mijostyn

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I believe both mass loading and CLD are applicable in certain situations.

I will side with Martyn as far as "box" enclosures are concerned. CLD is less effective with jailed panels. All you have to do is keep any resonances above the cut off frequency of the driver which can be done just by increasing the thickness of the material. Plywood is stiffer than MDF just much more expensive for cabinet grade.
For midrange drivers and above the best enclosure is no enclosure as Dalquist proved in the 70's. It is with baffle boards that CLD has a role. Two layers of solid surface material with a layer of stiff rubber in between makes a brilliant baffle board for midranges and tweeters. If you use a midrange that can function down to 125 Hz you can cross directly to subwoofers (never use just one.)

It is for woofers and subwoofers that enclosures become critical and it is here that mass loading can contribute to a good design. The ultimate enclosure would be a sphere but very difficult to make. Next is a cylinder. A decagonal  cylinder made of 1.5" plywood of the right volume as controlled by length and diameter makes a wonderful subwoofer enclosure. Better yet, if you put a driver in each end operating in phase you create a balanced force configuration. The enclosure does not vibrate at all. No additional mass required. The enclosure does not resonate because the walls are extremely stiff and they almost continuously vary in thickness from 1.5 to two inches.
With the advent of DSP room control, digital cross overs, very high powered amplifiers and wonderful subwoofer drivers sealed enclosures are the way to go. They are easier to build and smaller. Their performance is more predictable. Most important is they do not roll off as steeply under their Fs so they are easier to force down lower. With 12 inch drivers in a 4 subwoofer array using the fore mentioned enclosures and using digital bass management the system goes flat down to 15 Hz at 120 dB. This is a very interesting experience. The whole house sings. The rattles have rattles. Stuff goes walking off shelves (flour in the kitchen the most embarrassing.) It is as much fun as using launch control in a 911 Turbo.  Under control playing normal music such as the Dave Holland Quartet you would never know they are there and I cross over from ESLs at 125 Hz:)